Recognize problem spots in soybeans and take a soil test
Soybean cyst nematode is a yield robber, so the first step in managing SCN in the field is to test the soil to know that a population exists. It can cause up to 30% yield loss with no aboveground symptoms on the plants, and it has been found in 50 Nebraska counties, which produce over 80% of the state’s soybeans. Last year, SCN cost Nebraska farmers more than $25 million in lost revenue.
“Over the past five years, 2,700 samples have been processed, and just over 23% have come back positive for SCN,” says John Wilson, University of Nebraska Extension educator in Burt County. “SCN causes more yield loss than all other soybean diseases combined. Plots from the last four years show an average increase in yield of over 5 bushels per acre where SCN-resistant varieties were planted.
At a glance
• Soybean cyst nematode has been found in at least 50 Nebraska counties.
• Testing for SCN is the first step in management of the disease.
• Compare results from spots where plants look unhealthy to spots of normal growth.
“Soil samples can be taken any time of the year,” Wilson says. “One of the reasons after harvest is a good time is that fields may have looked fine, but yields were running less than expected.”
During harvest, farmers watch their combine yield monitors and may be able to identify problem spots that cannot be attributed to soil type, weed pressure or other problems.
“Sometimes we’ll have folks who will take samples in later July and August because they notice problem spots where soybeans seem stunted or wilted,” says Wilson. “Visually check the roots for cysts, but even if you don’t see any, you should also pull separate soil samples from the problem area and surrounding areas where plants look healthy.”
Plants in these little pockets may not be as tall as surrounding soybeans due to several factors, but when farmers observe these spots and are able to test the soil for SCN, it may help diagnose the problem, or at least rule out SCN if samples from the trouble area and adjacent soybeans are both negative.
How to proceed
“If you have a soil probe, starting from 3 to 4 inches to the side of a row, angle the probe about 8 inches deep with the tip of the probe underneath the center of the row,” says Wilson. “If you don’t know that SCN is in the field, sampling where you go through more of the root system makes it more likely to identify SCN if it is there.”
For narrow-row soybeans, it doesn’t matter as much because the top layer of soil is more uniform with soybean roots.
He suggests collecting 15 to 25 core samples in a field. If the field had lower-yielding areas or areas where plants didn’t look as healthy, sample those separately from the rest to see if one sample is positive and the other negative, or if one sample is higher in SCN.
Mix the core samples together in a bucket. Fill a soil sampling bag, available from local UNL Extension offices, with the soil mix. Record all information requested on the bag and ship as soon as possible to the lab.
Testing for SCN is easy and free, thanks to support from the Nebraska Soybean Board.
Worst-case robber: Soybean cyst nematode causes more yield loss than all soybean diseases combined, according to John Wilson (left), UNL Extension educator in Burt County.
This article published in the August, 2010 edition of NEBRASKA FARMER.
All rights reserved. Copyright Farm Progress Cos. 2010.